# Detect TCPSocket interruptions/disappearance

**URL:** <https://www.ruby-forum.com/t/detect-tcpsocket-interruptions-disappearance/168303>\
**Category:** Ruby\
**Created:** [May 19, 2009, 12:31pm UTC](https://www.ruby-forum.com/t/detect-tcpsocket-interruptions-disappearance/168303 "2009-05-19T12:31:40Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![reynar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e99b99/32.png) [@reynar](https://www.ruby-forum.com/u/reynar)\
**Post date:** [May 19, 2009, 12:31pm UTC](https://www.ruby-forum.com/t/detect-tcpsocket-interruptions-disappearance/168303/1 "2009-05-19T12:31:40Z")

</div>

Hi,

I am putting together a background daemon as part of a Rails app to  
handle monitoring of our phone system. The phone system exposes an TCP  
socket on which it delivers lines of text in real-time corresponding  
to events (new call etc).

I have put together a skeleton process to monitor this, shown below.  
However I am not sure how to reliably detect when the phone system  
goes away, say it is rebooted or similar.

In such a case the code simply hangs on the gets request within the  
loop and never returns.

When the phone system is visible again the original connection is  
either lost or timed-out, hence nothing is submitted for the daemon to  
receive. Ideally I need to detect this and re-open a connection via  
the daemon.

Is the gets method even the best method for this scenario?

I had considered having a separate thread monitoring the visibility of  
the server and if it disappears signal to cycle the connection.  
Although I’m sure there may be a better way…

Any thoughts much appreciated, Andrew.

begin

TCPSocket::open(“192.168.10.130”, 4005) do |socket|

```
$running = true

Signal.trap("TERM") do
  $running = false
  socket.close
end

socket.puts "LOGIN,\n"
if socket.gets == "LOGINOK\n"
  ActiveRecord::Base.logger.info "Successful Login, Start Monitor"
  while($running) do
    routing_message = socket.gets
    ActiveRecord::Base.logger.info DateTime.now.to_s + " " +

```

routing\_message  
end  
ActiveRecord::Base.logger.info “Stop Monitor”  
else  
ActiveRecord::Base.logger.info “Failed Login”  
end

end

rescue \*ErrorsOnSocket =\> err  
ActiveRecord::Base.logger.info “Socket Error, Retrying…”  
sleep 15  
retry  
end

---

<div class="post-metadata">

**Author:** ![reynar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e99b99/32.png) [@reynar](https://www.ruby-forum.com/u/reynar)\
**Post date:** [May 19, 2009, 3:46pm UTC](https://www.ruby-forum.com/t/detect-tcpsocket-interruptions-disappearance/168303/2 "2009-05-19T15:46:05Z")

</div>

Andrew E. wrote:

> I have put together a skeleton process to monitor this, shown below.  
> However I am not sure how to reliably detect when the phone system  
> goes away, say it is rebooted or similar.

Try setting SO\_KEEPALIVE on your socket.

It’s easier if you can send a periodic message to the far side and check  
you get a response within a second or two. However if you can’t do that

- i.e. you have to be an entirely passive listener - then SO\_KEEPALIVE  
sends periodic probes at the TCP layer. It may take a few minutes to  
detect that the connection has gone though.

---

<div class="post-metadata">

**Author:** ![reynar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e99b99/32.png) [@reynar](https://www.ruby-forum.com/u/reynar)\
**Post date:** [May 20, 2009, 2:42pm UTC](https://www.ruby-forum.com/t/detect-tcpsocket-interruptions-disappearance/168303/3 "2009-05-20T14:42:48Z")

</div>

> In such a case the code simply hangs on the gets request within the  
> loop and never returns.

Odd. If the socket closes then gets should return nil

So in this case the only way you know it closed is that…it goes away  
without notifying you?  
If that’s the case then some type of periodic liveness ping is the only  
way, I think (as Brian noted).  
-=r

---

<div class="post-metadata">

**Author:** ![reynar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e99b99/32.png) [@reynar](https://www.ruby-forum.com/u/reynar)\
**Post date:** [May 20, 2009, 3:04pm UTC](https://www.ruby-forum.com/t/detect-tcpsocket-interruptions-disappearance/168303/4 "2009-05-20T15:04:13Z")

</div>

Roger P. wrote:

> > In such a case the code simply hangs on the gets request within the  
> > loop and never returns.
> 
> Odd. If the socket closes then gets should return nil

Only if the far-end closes the socket normally. If the machine is just  
powered off or hard-resets, obviously no packet will be sent. And when  
it comes back up, it won’t know that it used to have an open connection.

If you send data _to_ it, it will respond with a RST. But this won’t  
happen if you’re just passively listening.